Find the answer and solution to this math problem Find the answer and solution to this math problem

Both should be brought in, and after finding x, see if it matches the range.

Bringing f(x)=2 into f(x)=3 x gives x=log3 2<1 coexistence.

Bringing f(x)=2 into f(x)=-x gives x=-2<0 is not a conformity.

So x=log3 2

f(x)=-x(x>1), since f(x)=2, then x>1 is impossible because f(x) is negative when x>1.

Therefore, x"=1 substitution obtains.

3^x=2,x=log(3)2<1

So x=log3 2

It would be enough to discuss it in two cases:

1) If x < 1 and 3 x = 2, we can solve x as the logarithm of 3 base 2, and we can know that this solution is less than 1, so this number is a solution of x.

2) If x>1 we can see that f(x) is <-1, then f(x) cannot be equal to 2 In summary, x is equal to the logarithm of 2 with 3 as the base.

When x>1, -x<-1, then f(x) cannot be equal to 2, so only 3 x=2, x=log is the logarithm of base 2 with 3.

The general practice of this problem is to make each formula of the piecewise function equal to the given value (this problem is equal to 2). After finding the value of x, you can compare the given segment definition domain with the value in this definition field.

This question can also be judged first:

When x>1 --f(x)<-1, it follows from the known condition f(x)=2 that x should be the value in the domain defined in the first paragraph.

i.e. 3 x=2 --x=log(3)2

If the condition of x<=1 is satisfied, there is only one solution to this problem x=log(3)2

Because x>1 is fx<-1 and fx=2, x<=1, i.e., 3 x=2, x=log(3)2, and the condition of x<=1 is satisfied.

A total of 6,818 people participated, and the 231st contestant accounted for 3%.

This problem belongs to the proportion problem in primary school math problems, which can be obtained by dividing his ranking by the total number of people.

This question is more than 100% because there are too many people to understand the numbers and answers.

(1) If the quantity of the increase in the price of each piece is m, and the daily sales volume of the product is n, then m=n

2) Let the daily profit be w, w=(130-120+m)*(70-n)=1600

Because m=n, n=m=30 so the price of each piece is 160 yuan, and the daily profit can reach 1600 yuan.

(1) Let the quantity (yuan) of the increase in the price of each piece be m, and the quantity (pieces) of the decrease in daily sales will be n, because for every increase in the price of each piece, the daily sales will be reduced by one piece. So m=n(2) and set the daily profit to y

y+120*（70-n）=130m

y+8400-120n=130m

m=n so y=250m-8400

1600=250m-8400m=4

Solution: If the total amount in the pool is x, the water inlet rate of the inlet pipe is x 20The speed of one outlet pipe is x 45

When the four pipes are opened, 3*x45-x20=x 60That is, the water velocity is x 60

There is 60% water in the pool, and when there is 20% water left, a total of 40%x flows out.

40% x (x 60) = 24 minutes.

That is, after 24 minutes, 20% of the pool water is left.

For any plane ax+by+cz=d, its normal vector is (a, b, c), and the hall is premature.

Therefore, the plane 2x-3y+z-1=0, and its normal vector is (2,-3,1), choose a

There must be something wrong with this question.

You set the four boxes to x, y, a, b, then:

x-y=9 (1)

a-b=14 (2)

x+a=12 (3)

y+b=2 (4)

1) + (4) get.

x+b=11 (5)

2) + (5) get.

x+a=25

This contradicts equation (3).

This question is not valid.

The first digit cannot be less than 9, and the second number in the first column cannot be greater than 3, and this number cannot be less than 14 for the second row, which is contradictory and unsolvable!

Let the unknowns, solve the equation, and have no solution.